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Since the Watson-Crick model of our double helical structure DNA in 1953 and the foundations of the central dogma of molecular biology (DNA-RNA-protein) were established, major advances in genetics have taken place. In the year 2003, the Human Genome Project finished an accurate and complete sequence of the human genome which became available to scientists and researchers (and for you if you wish) to download at the NHGRI page. Knowledge of the complete sequence allows the identification of all human genes, the variation of such genes among different populations and provides a fundamental understanding of how our genome contribute to health and disease. Now, with the use of genetic engineering it is possible to produce insulin, EPO or monoclonal antibodies among other uses through gene modification. But with this genetic "revolution" taking place, have we finally deciphered who we are? Are we just the molecular result of the laws of heredity?

The mysteries of heredity have always fascinated scientists. Identical twins share the same genotype, the same womb and they are usually brought up in a very similar environment. So, if they share the same genetic code, how is it possible that they can become so different as they grow? Why are there differences in susceptibilities to mental diseases such as schizophrenia or bipolar disorder? Although monozygotic twins share a common genotype, most MZ twin pairs are not identical, theres is a phenotypical discordance. Modern twin studies, are focusing now on showing the effect of a person's shared environment (family) vs. a unique environment (the individual events that shape a life) on a trait. According to the research by Esteller and Craig, it has been concluded that even genetically identical twins are epigenetically distinct at time of birth and these epigenetics differences become more pronounced with age and exposure to different environments.

So, how does environment plays a role in this differences? Why are some foods good for our health and why do others cause us disease? What is the impact of stress in our health? What role does environment play in cancer? Why is it that the older we get, we are more susceptible we are to develop certain diseases? Why do we age? Why and how does one of our X-chromosomes (in females obviously) becomes deactivated? What role does stress play in child development? So many debatable and interesting questions to solve.

Welcome to the fascinating world of EPIGENETICS!!! The debate where Nature vs Nurture takes place and become one.

Epigenetics is an emerging frontier of science that involves the study of changes in the regulation of gene activity and expression that are not dependent on gene sequence and it is in "The Epigenetics Revolution" by Nessa Carey where you will be introduced to a fantastic world of science in which you will learn if and how environment play a fundamental role in your genotype/phenotype.

Epigenetic mechanisms play a key role in regulating gene expression (by turning "off" and "on" genes) such as stable transcription complexes, modification of histones in chromatin, lysine acetylation and methylation of DNA. These are basic concepts you will read throughout the book in order to understand this fascinating field of study.

One hallmark of these modifications and probably the better understood so far is DNA methylation which affects your genome. Methylation simply means the addition of a methyl group at cytosine, which is the only of the four DNA bases that gets methylated and more specifically at the C's that preced G's in the DNA chain and form what we refer to as CpG dinucleotides or "islands" when there are high concentrations. Once DNA is methylated it bind to a protein called MeCP2, then these methyl groups turn genes off by affecting interactions between DNA and the cell's protein-making machinery such as gene promoters, transposons and imprinting control regions. In the following picture you can see how MeCP2 binds to a gene promoter attracting other proteins to help switch the gene off:

One of these important regulatory roles of DNA methylation is genomic imprinting. Imprinting is a normal process caused by alterations in chromatin that occur in the germline of one parent, but not the other, at characteristic locations in the genome. A process that takes place during gametogenesis and persists postnatally into adulthood through hundreds of cells divisions so that only one maternal or paternal copy of the gene is expressed. Once again, imprinting affects the expression of a gene but not its primary DNA sequence. You will also have a voyage in the world of imprinting disorders such as Prader-Willi, Angelman Syndrome, Silver-Russell syndrome and Beckwith-Wiedemann syndrome among other essential ones. If you are a doctor, you will enjoy it as a good refresher.

The second kind of epigenetic mark, called histone modification, indirectly affects the DNA in your genome. Histones are spool-like proteins that enable DNA's very long molecules to be wound up neatly into chromosomes inside the cell nucleus. A variety of chemical tags can grab hold of the tails of histones, changing how tightly or loosely they package DNA. If the wrapping is tight, a gene may be hidden from the cell's protein-making machinery, and consequently be switched off. In contrast, if the wrapping is loosened, a gene that was formerly hidden may be turned on. The following image is a representation of a core nucleosome with its respective histones and around 200 base pairs:

Why is epigenetics important to you? Why does it matters? According to the NHGRI: "Lifestyle and environmental factors can expose a person to chemical tags that change the epigenome. In other words, your epigenome may change based on what you eat and drink, whether you smoke, what medicines you take, what pollutants you encounter and even how quickly your body ages. There is also some evidence from animal and human studies that indicates that what a female eats and drinks during pregnancy may change the epigenome of her offspring.Most epigenomic changes are probably harmless, but some changes may trigger or increase the severity of disease. Researchers already have linked changes in the epigenome to various cancers, diabetes, autoimmune diseases and mental illnesses."

As you can see, Epigenetics is an area of increasing importance in human and medical genetics with significant influences on gene expression and phenotype, both in normal individuals and in a variety of disorders. The author does a wonderful work, in explaining the basic concepts of this field in science including molecular mechanisms involved, essential genes and syndromes seen in medical genetics as well as a wonderful tribute to the work of various scientists (from Gregor Mendel's laws of inheritance to Shinya Yamanaka's stem cell research) involved in what we understand today regarding genetics.

If you are familiar with the terms and this field of study, perhaps you will find the same information as other books or publications as you will go over the typical examples like the agouti mouse experiments, the classic Dutch famine and its correlation with obessity, the epigenetics of the royal jelly, etc... but I think is still enjoyable to re-read if you love the topic. For this reason I give a 4star, much of the information I was already familiar with. Besides, she did not mention the work of the Nobel laureates Barbara McClintock or Paul Berg which I consider essential here.

It is a book good enough for anyone with the desire to learn and perhaps and opportunity to impress your science literate friends next time they speak of epigenetics! Jump in and learn more about this amazing field!

For more information please visit:- National Human Genome Research Institute: http://www.genome.gov/- OMIM (Online Mendelian Inheritance of Men) Which is an Online Catalog of Human Genes and Genetic Disorders: http://omim.org/.